Ferrimagnetic couplers employing a transition from air dielectric waveguide to solid dielectric waveguide



Nov. 12, 1968 w, M. HONIG ETAL 3,411,112

FERRIMAGNETIC COUPLERS EMPLOYING A TRANSITION PROM AIR DIELECTRIC WAVEGUIDE TO SOLID DIELECTRIC WAVEGUIDE ril 15 966 FIG. 2 FIG. 3

Fl g DIELECTRIC WAVEGUIDE 1 N VENTORS WILLIAM M. HON IG Y EDWARD I WROBEL ATTORNEYS United States Patent FERRIMAGNETIC COUPLERS EMPLOYING A TRANSITION FROM AIR DIELECTRIC WAVE- GUIDE TO SOLID DIELECTRIC WAVEGUIDE William M. Honig, Brooklyn, N.Y., and Edward J.

Wrobel, Orlando, Fla., assignors to Loral Corpogrgrtitin, New York, N.Y., a corporation of New Filed Apr. 15, 1966, Ser. No. 542,957 Claims. (Cl. 333-24) ABSTRACT OF THE DISCLOSURE Apparatus for coupling RF energy to a ferrimagnetic resonator by means of waveguides comprises two opposing solid dielectric waveguides abutting against opposite sides of a YIG sphere. The product of the dielectric constant (e) and permeability t) of the solid dielectric is approximately equal to the product of the dielectric constant and permeability of the YIG sphere for a range of frequencies including the resonant frequency of the sphere. Means are provided for coupling the RF energy from a standard air dielectric waveguide to one of the solid dielectric waveguides and for coupling energy from the other of the solid dielectric waveguides to a second air dielectric waveguide.

The present invention relates to a device for coupling RF energy to and from a ferrimagnetic resonator.

Ferrimagnetic resonators are used for many purposes in the microwave arts. Recently, extremely low loss materials in the form of small spheres 0r discs have been used as microwave ferrimagnetie resonators for limiting, filtering and other related purposes. By Way of example, such low loss materials may include yttrium iron garnet (YIG), gallium yttrium iron garnet (GAYIG), and other known materials.

The operation of ferrimagnetic resonators requires the application of a magnetic field which, in accordance with known theory, determines the resonant frequency of its equivalent high Q resonator. Application of the field presents no particular problems where coaxial type transmission lines are used. However, at frequencies above approximately 12 gHz. coaxial lines are generally useless due to the excitation of higher order modes, and it is necessary to couple energy to the resonator by waveguide.

In applying the magnetic field, it is desirable to maintain a very homogeneous field across the sphere and to minimize the length of the air gap, which determines the power necessary to establish a given magnetic field. Also, fringing of the field is a linear function of the gap, thereby requiring larger diameter pole faces to reduce the magnetic field gradients across the sphere. Larger fields further lead to saturation of the magnet and make for non-linear tuning and increased leakage flux, requiring larger shielding structures. The increased inductance in a large number of ampere turns required is another undesirable byproduct of a larger air gap. Power supply transistors must be rated higher in power and breakdown voltage, and practically every parameter of the filte-r suffers to one degree or another.

In the case of a conventional air dielectric waveguide, the minimum size of the Waveguide is dependent upon frequency, and the air gap will always be of such size as to present problems due to the above considerations. Moreover, tight coupling is difficult to achieve because of the small filling factor. As a result, substantial losses may be associated with the prior art structures.

Accordingly, the main object of the invention is to provide a device for coupling to a ferrimagnetic resonator wherein the air gap for the magnetic field is substantially reduced.

Another object of the invention is to provide a device for coupling to ferrimagnetic resonator with tighter coupling than prior art structures.

In the drawings:

FIGURE 1 is a detailed top view of the portion of the invention which couples to the ferrite sphere;

FIGURE 2 is a side sectional view along the line 22 of FIGURE 1;

FIGURE 3 is a detailed top view of a portion of the invention as it may be used with crossed waveguides;

FIGURE 4 is a side sectional view along the line 44 of FIGURE 3;

FIGURE 5 is a top sectional view showing how conventional waveguide is matched to the transmission line of the invention;

FIGURE 6 is a side sectional view of the coupling structure of FIGURES l and 2 in combination with conventional Waveguide;

FIGURE 7 is a top sectional view of another matching structure similar to FIGURE 5;

FIGURE 8 is a side sectional View along the line 8-8 of FIGURE 7; and

FIGURES 9 and 10 are top and side views, respectively, of a third matching structure which can be used with the invention.

According to the invention, and as shown in FIGURES 1 and 2, a ferrimagnetic resonator consisting of a YIG sphere 10 is situated within a waveguide comprising solid dielectric portions 12 and 14 and an outer conductive coating 16. The solid dielectric material may be TiO or SrTiO A conductive rim 18 extends transverse of coating 16 and into contact with the periphery of sphere 10. The direction of the applied magnetic field is shown by the arrow H and, by way of example, may be produced across pole faces 19 and 21.

The solid dielectric of waveguide portions 12 and 14 has a high dielectric constant. Since the dimensions of waveguide vary inversely as e, where e is the relative dielectric constant of the waveguide dielectric, it is possible to substantially reduce the waveguide dimensions required for a given frequency range. For example, if rutile (TiO is selected as the dielectric, waveguide having dimensions of 21.5 10.7 mils (thousandths of an inch) may be employed for the 26 to 40 gHz. (40,000 mHz.) region, as opposed to a required size of 280x mils in the case of air dielectric waveguide. This then is a reduction in waveguide dimension by a factor of almost fourteen which permits the gap dimensions between pole faces 19 and 21 to be similarly reduced.

The reduced size of the waveguide also concentrates the microwave energy into a much smaller volume, thus effectively increasing the filling factor and permitting much tighter coupling to the resonator. The conductive rim 18 between waveguide portions 12 and 14 tends to prevent leakage of the energy from the input to the output.

Since the ferrimagnetic sphere 10 touches both dielectric sections 12 and 14 on opposite sides, it forms a path for the microwave energy provided that the product of the dielectric constant (e) and permeability (,u) of the sphere is substantially equal to that of the waveguide. By way of example, suitable dielectrics may have dielectric constants in the range of 200-300 and a permeability of approximately one. The ferrimagnetic sphere 10, on the other hand, will normally have a dielectric constant between fifteen and twenty and a permeability which ranges between one and three hundred depending upon how close the sphere is to ferrimagnetic resonance, with the maximum occurring at resonance. Thus, there is a substantial range of values on either side of the resonant frequency where the above criterion is satisfied so that microwave energy can be propagated from dielectric to sphere to dielectric. Off resonance, the criterion is not met, and the sphere behaves to some extent as waveguide beyond cut off, the larger attenuation constituting off-band rejection.

Because of the substantial difference in dielectric constant between the solid waveguides 12 and 14 and the surrounding air, it is not necessary that the waveguide be coated with a conductor 16, since the radical change in dielectric constant will prevent microwave energy from passing into the air. Also, dielectric 12 and 14 need not fully envelop sphere 10 as illustrated, and for many purposes it will be sufficient if the dielectric waveguides merely abut against opposite ends of the sphere 10. It is further unnecessary that sphere 10 be smaller in diameter than one or both of the waveguide dimensions, and the principles of the invention are equally applicable to solid dielectric waveguides in which the width and/or height is less than the sphere diameter.

In FIGURES 3 and 4 the invention is shown in use with a. crossed waveguide structure wherein an upper guide 20 is transverse to a lower guide 22. As in the case of FIGURES 1 and 2, Waveguides 20 and 22 are made of a solid dielectric such as rutile, with the YIG sphere 10 located at the common wall of the two guides. Again, the junction of the Waveguides and the outer surfaces thereof may be coated with silver or some other conductor to reduce radiation, but the invention contemplates the use of waveguides which are not so coated.

FIGURES and 6 show a matching structure for coupling energy from conventional air filled waveguide 24 to a solid dielectric waveguide 26. Waveguide 24 includes an end wall 27 into which the solid dielectric Waveguide 26 is inserted. The end of waveguide 26 within the guide 24 is pointed as shown at 28 to facilitate passage of the microwave energy into the dielectric 26. Pointed portion 28 should be between about one and four times the operating wavelength. FIGURE 6 shows how the coupling portion of the FIGURES 1 and 2 may be combined with the matching structure of FIGURE 5.

An alternative matching structure for coupling the energy from the waveguide 24 to the solid dielectric 26 is shown in FIGURES 7 and 8. In this instance, only one end of guide 26 is tapered.

A third coupling arrangement is shown in FIGURES 9 and wherein a waveguide 30 includes a tapered end 32 terminating in a short vertical edge 34. The solid dielectric waveguide 26 abuts against the short wall 34 to receive a portion of the microwave energy propagating through guide 30.

In this specification and the attached claims no distinction is intended to be made between the words ferromagnetic and ferrimagnetic, there being an apparent lack of agreement in the art as to the scope of the re spective words.

What is claimed is:

1. A device for coupling microwave energy to a ferrimagnetic resonator including a sphere of ferrimagnetic material, comprising first and second air dielectric waveguides, first and second solid dielectric waveguides in contact with said sphere at different portions thereof, the cross-sectional area of said solid dielectric waveguides being substantially less than the cross-sectional area of said air dielectric waveguides, means adjacent opposite surfaces of said solid dielectric waveguides for applying a magnetic field across said sphere, and matching means for coupling energy between said air dielectric waveguides and respective ones of said solid dielectric waveguides, the dielectric constant of said solid dielectric being substantially higher than air, the product of the permeability and dielectric constant of said solid dielectric being approximately equal to the product of the dielectric constant and permeability of said sphere for a range of frequencies including the resonant frequency of said sphere such that microwave energy in said range of frequencies can be coupled between said waveguides through said sphere.

2. A device according to claim 1, wherein said solid dielectric waveguides include a conductive coating.

3. A device according to claim 1, wherein said solid dielectric comprises T iO or SrTiO 4. A device according to claim 1, wherein said solid dielectric Waveguides include indentations for receiving said sphere, said solid dielectric waveguides substantially enveloping the entire sphere.

5. A device according to claim 4, further including a conductive layer between said solid dielectric waveguides.

References Cited UNITED STATES PATENTS l/1959 Wilkinson 333-34 X 1/1967 Blau et al 33324.2 

